Experimental investigation into the effect of supports and overhangs on accuracy and roughness in laser powder bed fusion

Overhangs are one of the most critical features in the design of parts for Powder Bed Fusion. In particular, accuracy and roughness of these geometrical elements are the main concerns while designing for this process. Support structures are the most common solutions adopted to preserve the quality of overhangs and ensure the appropriate completion of the whole process. This work aims to correlate geometrical parameters of overhangs and supports to the distortion and roughness of parts. For this purpose, an experimental campaign is carried out on specimens manufactured via a powder bed fusion of stainless steel. Appropriate process parameters have been chosen thanks to preliminary experimental tests. Both displacement and roughness are measured using optical and contact systems. The two methods show considerable differences that are examined in the light of process features. The analysis of results highlights that the design of support structures has to be carried out in accordance with the thickness and inclination of the overhangs in order to minimise distortions. Local defects occurring on the edges are also highlighted by comparing contact with optical measurements. An upward warping of all the geometries is observed after annealing. Roughness underlines the fact that the inclination of surfaces is the only influential factor, since the support design can efficiently dissipate the thermal energy from the overhangs. Comparative analysis of contact and optical measurements also highlights the limitations of the first type of measurements in detecting small surface defects.